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#include <iostream>
#include <deque>
#include <fstream>
#include <vector>
#include <cstdint>   // pentru int64_t
using namespace std;

int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");

    int n, k;
    f >> n >> k;

    vector<int> a(n);
    for (int i = 0; i < n; i++)
    {
        f >> a[i];
    }

    deque<int> dq; 
    int64_t sum = 0; // sumă pe 64 biți (poate depăși int)

    for (int i = 0; i < n; i++)
    {
       
        while (!dq.empty() && a[dq.back()] >= a[i])
        {
            dq.pop_back();
        }
        
        dq.push_back(i);
        
        if (dq.front() <= i - k)
        {
            dq.pop_front();
        }

        if (i >= k - 1)
        {
            sum += a[dq.front()]; 
        }
    }

    g << sum;
    return 0;
}